"Intelligent" resize

I want to save resources on a linux webserver and want to write a short bash-
script, that reduces filesize before the files are imported into a Menalto 
Gallery. I know how to do this with a bash-script, but I assume a lot can be 
done with IM directly. 

First the original files are uploaded to the webserver in original size, but 
in different folders.

like
/incoming/original/topic1/1.jpg
/incoming/original/topic1/2.jpg
/incoming/original/topic1/subtopic1/3.jpg
...

Then convert should be used to get:
/incoming/reduced/topic1/1.jpg
/incoming/reduced/topic1/2.jpg
/incoming/reduced/topic1/subtopic1/3.jpg

Can IM be used to create this files directly or do I have to use a loop?

The images are in portrait and landscape format. Is it possible that the 
longest side is always 2000 pixels without doing an analysis before with 
identify? Can images with a lower resolution than 2000 be excluded from 
convert?


Thanks

Al